To transmit messages in secret.
Numbers are used in zip codes.
cypher codes
Device codes on televisions are used for communications between the television and the remote control. The codes are used to setup and change channels.
AnswerDelivery codes.
Any membership codes that are posted would have been used, and membership codes can only be used once.
E codes
e
You can't. only three codes were possible, And they were already used.
Category III codes
HCPCS codes are used in the medical system to identify products. They also can be used to identify supplies and services.
codes that can no longer be used
Game shark codes